Nitrate sensors are becoming increasingly important tools for water and soil quality monitoring and resource management. Ultraviolet (UV) absorption sensors are today's standard for water quality analysis (Pellerin, et al., “Optical Techniques for the Determination of Nitrate in Environmental Waters: Guidelines for Instrument Selection, Operation, Deployment, Maintenance, Quality Assurance, and Data Reporting: U.S. Geological Survey Techniques and Methods,” USGS, Vol. 1-D5 (2013), and, Sah, “Nitrate-nitrogen Determination—A Critical Review,” Commun. Soil Sci. Plant Anal., vol. 25, pp. 2841-2869 (1994)).
Unfortunately, UV sensors capable of delivering continuous data during prolonged deployment periods not only cost between $15,000 and $25,000, but are also vulnerable to interference from inorganic and organic substances that absorb light at wavelengths similar to those of nitrate. These substances include nitrite, bromide and chromophoric dissolved organic carbon (DOC), which are common in both water and soil.